Dental chair.



No. 642,405. Patented Ian. 30,1900. B. M. WILKERSON.

DENTAL CHAIR.

(Application filed July 21, 1899.)

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(No Model.)

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Patented Ian. 30, I900.

B. M. WILKERSON.

DENTAL CHAIR.

(Application filed July 21, 1899.)

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(liq Model.)

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Patented Jan. 30; I900.

B. M. WILKERSON.

DENTAL CHAIR.

(Application filed July 21, 1899.)

5 Sheets-Sheet 3.

(No Model.)

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No. 642,405. I Patented Jan. 30, I900;

B. m. WILKERSON.

DENTAL CHAIR.

(Application filed July 21, 1899.)

5 Sheets-Shegt 4.

(No Model.)

WITNESSES:

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B. m. WILKERSON.

DENTAL CHAIR." [Application filed :m1' 21, 1399.

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(No Model.)

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UNITED STATES Fries.

PATENT BASIL M. W'ILKERSON, OF BALTIMORE, MARYLAND, ASSIGNOR TO THE S. S. W'I-IITE DENTAL MANUFACTURING COMPANY, OF PHILADELPHIA, PEN N SYLVANIA.

DENTAL CHAIR.

SPECIFICATION forming part of Letters Patent No. 642,405, dated January 30, 1900.

Application filed July 21, 1899- To all whom it Woo/y concern:

Be it known that I, BASIL M. WILKERSON, a citizen of the United States, residing in the city of Baltimore and State of Maryland, have invented certain new and useful Improvements in Dental Chairs; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

My invention relates to dental chairs; and it consists in certain improvements principally in the back and foot rest sections thereof.

The object of my present invention is to improve some of the sections of the dental chair, shown in United States Letters Patent No. 581,670, granted to me April 27, 1897.

In the accompanying drawings, which-show a suitable embodiment of my presentimprovements, Figure 1 is a view in side elevation of a dental chair, showing myimproved leg and foot rest section in its lowest as well as its highest position and with the backrest section broken away. Fig. 2 is a top or plan view of the dental chair with the back-rest section and the upholstered seat-pad omitted. Fig. 3 is a similar view with the leg and foot rest section omitted and also showing a'somewhatmodified seat-frame. Fig. 4 is a view in vertical central section of the chair with the base or supporting portion omitted and with a portion of the back-rest section and a portion of theleg and foot rest section also omitted. Fig. 5 is a View in rear elevation of the main'controllin g-rod of the leg and foot rest section detached. Fig. 6 is a view in'rear elevation of my improved back-rest section. Fig. 7 is a central vertical sectional view of said backrest section, showing a portion of the seatframe of-the chair to which said back-rest section is attached. Fig. 8 is a view in side elevation of a modified form of foot-rest. Fig. 9 is a view, partly in plan and partly in horizontal section, of a modified form of rockshaft for actuating the pawl of the leg and foot rest section. Fig. 10 is a detail sectional view showing one of the recesses for the side arms of the footboard-supporting frame.

That portion of the chair usually termed the foot-rest section comprises a footboard,

Serial No. 724,662. (No model.)

tained at all times practically in parallelism with said seat, so that when the footboard or platform is raised to the level of the seat it will form practically an extension thereof, and when in such position it comes into play as a leg-rest. The back-section and the headrest section (which latter section is not herein shown) are likewise capable of being adjusted to a level with said seat-section of the chair, whereby when all the sections of the chair-body are brought into alinement the chair is virtually transformed into what is tantamount to a couch, or the anesthetic position, as it is called by dentists.

For the purpose of convenience all positions of the back and the footboard when the same are not in alinement will herein be referred to as the operating positions, because these positions provide only for dental operations. The positions of these parts when in alinement or in approximate alinement will be referred to as the anesthetic position, because such position meets the requirements and incidents of anesthesia.

As the foot-rest carried by the footboard or platform normally occupies a position above the level of said footboard or platform, it is obviously desirable when the chair is temporarily transformed into a couch, as above indicated, that the foot-rest should also assume an inoperative position in alinementwith the other sections of the chair-body or drop to or below the level of the footboard, where it'will be out of the way and not interfere with the feet of a person under the influence of an anesthetic. Besides generally improving the construction of thefootboard and its operating mechanism I have also provided mechanism whereby whenever the footboard is elevated to its uppermost position the foot-rest, as just stated, is caused to automatically drop to a level with the footboard and whenever the footboard is lowered the foot-rest automatically assumes its normal operative position.

I will first proceed to describe the improved leg and foot rest as follows: Curved side arms A A, constituting the supporting-frame of the footboard, are hinged or pivoted at or near their upper ends at a a to the opposite inner sides of the seat-frame B of the chair, near the front of said seat-frame. The side arms are shown as being connected by a central plate, screen, or apron A, which may be cast integral with said arms or made separate therefrom, as may be desired. A footboard or platform 0 is hinged at its inner end to the lower end of the side arms A A at a CL. A foot-rest D is carried at the outer end of the footboard and is pivoted thereto by way of its side arms D D at d (1, the foot-rest being adapted to project above the footboard at all times save when the footboard is in its uppermost position on a level with the seat of the chair or when it is independently dropped to or below the level of the footboard, as will be hereinafter explained. A supplemental foot-rest D may be pivoted by way of its side arms D D to the outer end of the foot-rest at cl cl and is capable of being rocked into either of two operative positions nearer to or farther away from the chair -seat. A controlling-rod E, preferably triangular in shape and of skeleton form and which willbe herein referred to as the main controlling-rod, is pivoted at its upper broad end at e e to the lower ends of brackets E E, secured to the inner opposite sides of the seat-frame B, and at its lowerend the main controllingrod is pivotally connected at c to the lower end of a link E pivotally connected at its opposite end to the pivot-rod a, connecting the side arms A A and the footboard. The distance between the pivots a and e is the same as the distance between the pivots a and e. Notched lugs O 0, depending from the inner end of the footboard, are adapted to engage the pivotbolt 6, which unites the main controlling-rod and the link E Thus the main controllingrod may be said to be pivotally connected to the footboard at the point e, and the construction is such that the parallelism of the footboard relatively to the chair-seat is preserved in whatever position of vertical adjustment said footboard may be placed. At the same time, owing to the peculiar construction of the pivotal connection between the main controlling-rod and the footboard, the latter may be folded up against the supporting-frame and the foot-rest turned over and down upon the chair-seat without disturbing the pivotal connection between the supporting-frame and main controlling-rod and the footboard. The purpose of this adjustment is chiefly to enable the chair to be conveniently packed for transportation and also for moving the footboard out of the way when desired. \Vhen the footboard and foot-rest are folded up, as just described, the notched lu s C 6 leave their hearing on the pivot e,

which is held in proper position by the link E so that when the footboard is again lowered to its operative position the notched lugs will necessarily find their proper bearings.

A secondary controlling-rod F is located beneath the footboard and is sustained in proper horizontal position and is adapted to have a slight endwise-sliding movement at or near its inner end in a stirrup (J on the under side of the footboard. The secondary controlling-rod has pivotal connection at its outer end with the foot rest D, a short distance below'its pivotal connection (Z with said footboard, by way of a lug or lugs 61 on said foot-rest. The inner end of the secondary controlling-rod is shown as being enlarged to form a head F, adapted to bear against a rounded projection E of the main controllingrod, said projection extending a short distance forward of the pivot e of said main controlling-rod. By this construction it will be seen that as the head of the secondary controlling-rod bears against the projection E of the main controlling-rod the foot-rest is caused to normally project above the surface of the footboard in operative position, that when the footboard is raised to the level of the chair-seat to constitute a leg-rest, as before described, the movement of the projection E permits the secondary controllingrod to move inwardly, whereby the foot-rest is caused to drop to or below the level of the footboard to itsinoperative position, and that when the footboard is lowered the projection E? acts upon the secondary controllingrod to cause the foot-rest to automatically resume its operative position above the level of the footboard. This construction also allows of the footboard being folded up, as before described, the head of the secondary controlling-rod being free to leave the projection E when the footboard is folded and being assured of coming in proper contact with this pro jection when the footboard is lowered again. In addition to automatically raising and lowering the foot-rest relatively to the footboard by movement of the latter I have also provided means for enabling the foot-rest to be dropped to or below the level of the footboard independently of the movement of said footboard and in whatever position the same may occupy. The preferred manner of accomplishing this is as follows: Instead of pivoting the forward end of the secondary controlling-rod F directly to the lug or lugs d of the foot-rest I have provided a toggle-connection, as follows: The lugs d are on opposite sides of the center of the foot-rest and a pivot-rod G passes through them. Pivoted upon said rod G, near the lugs 01 are links G, through the opposite ends of which passes a rod G the forward forked end of the secondary controlling-rod being pivoted to said rod G \Vhen the foot-rest is in its operative position above the footboard, as shown in the lower footboard, Fig. l, the toggle connection is straightened out,the links G resting against the under side of the secondary controllingrod, and the foot-rest cannot be moved downwardly. By slightly depressing the secondary controlling-rod by means of its operatinghandle F the toggle connection is broken or opened and the foot-rest is permitted to drop below the upper surface of the footboard into an inoperative position, as shown in the upper footboard, Fig. 1. A coiled spring H, connecting the footboard and the secondary controlling-rod, serves to assist in restoring the foot-rest to its upright operative position and to return the toggle to its closed position, which may be accomplished by simply grasping the foot-rest and lifting it. A rubber plug or plugsf may be secured upon the footboard, and when the foot-rest drops the lugs d strike against these plugs, whereby all noise and jar are prevented. The object in thus dropping the foot-rest below the upper surface of the footboard when the same is in its lowest or medium positions, or, in other words, when the footboard is in any of its operating positions, is to place it beyond the reach of the feet of a patient seated in the chair in order to 'prevent the patient from kicking or bringing undue pressure to bear upon the foot-rest when undergoing painful operations or when under the influence of an anesthetic. The operating-handle F of the secondarycontrolling-rod may be depressed to drop the footrest either by hand or foot, as desired.

In Fig. 81 have shown a modification of the connection between the footboard and footrest for permitting the latter to be dropped and in which the toggle lever is omitted. This connection may be described as follows: Lugs d are formed on the foot-rest, as before, and are connected by a rod C1 The outer ends of the secondary controlling-rod F are formed with lower notches f, upper notches f and suitable cam-surfaces, as shown in the drawings. When the rod (1 rests in the lower notches f, the foot-rest is in its upright operative position. By depressing the secondary controlling-rod F, as before explained, the lower notches f will leave the rod (Z and the foot-rest will drop until the rod 01 comes to rest in the upper notches f the foot-rest being thus held in its inoperative position on or below the level of the footboard. The footrest may be restored to its normal operative position by simply lifting it, as before, until the rod (1 rests in the lower notches f. will be understood that the spring H should be employed, as in the preferred form. The rod d acting upon the cam-like surfaces of the notched secondary controlling-arm, provides for an easy and gradual stopping of the foot-rest, which may thus be dropped without shock or jar and without the employment of the rubber plugs f. (Shown in Fig. 1.)

It will of course be understood that with the herein-described organization of footboard and foot-rest the foot-rest is automatically placed in an inoperative position whenever the footboard is moved to its uppermost or anesthetic position and that the foot-rest .may also be placed in a similar inoperative position when desired even when the foot-- board is in its lowest or any of its operating positions. Obviously this latter adjustment of the foot-rest may be used in an organization in which the automatic movement of the foot-rest is omitted.

The footboard may be locked and sustained in any position to which it may be vertically adjusted by means as follows: A pawl I, pivoted to or between lugs or brackets a pro- ,jecting from the central plate or screen A of the footboard-supporting frame, is adapted to engage with the teeth of a ratchet-plate E connected to or formed with the main controlling-rod E. A weighted arm or extension I of the pawl serves to normally hold the pawl in engagement with the ratchet-plate. The pawl is keyed upon a rock-shaft I having bearing at one end in said lugs orbrackets a and projecting to one side of the supporting-frame, in which its opposite end has bearing. An operating pedal or handle J is provided for the rock-shaft I and is located on the outside of the footboard supporting frame. Instead of securing the operatinghandle directly upon the rock-shaft I, upon which the pawl is keyed, I prefer to key it upon another rock-shaft J, parallel with the rock-shaft I and having bearingin a projection a of the side frame A. A lever J keyed upon the rock-shaft J, is connected with a lever 1 keyed upon the rock-shaft I by means of a link J whereby the movement of the operating-pedal may be transmitted to the pawl I. The operating pedal or handle J, which extends on opposite sides of the rockshaft J, may be operated either by the hand or foot and servesas the means for actuating the pawl and also for raising and lowering the footboard.

The weight of the footboard and parts carried thereby is counterbalanced by a coiled spring K, which is connected atone end to a projection E on one of the brackets E and at its opposite end is connected to the main controllingrod E. The tendency of this spring is to pull the footboard upwardly, whereby the same may beraised and lowered with comparative ease.

When it is desired to raise the footboard, the operators foot or hand is placed upon the operating-handle of the pawl J and a slight pressure upon the inner end of said handle serves to rock the pawl out of engagement with the ratchet and further downward and forward pressure upon the handle will elevate the footboard. Upon relieving the handle of pressure the pawl, owing to the action of its weighted arm, will immediately engage the ratchet and lock the footboard in any position to which it may have been elevated. To lower the footboard, the pawl is tripped, as before, and the footboard allowed to descend to the desired position. It will be observed that the operating-handle is located at or near the bottom of the footboard-supporting frame,

, practically on a level with the footboard, in

convenient reaclrof the operators foot and that when it is desired to but slightly change the vertical position of the footboard it can most conveniently be accomplished by means of the said operating -handle. Obviously, however, the footboard may be elevated to any desired point by grasping it and lifting it bodily without operating the controlling lever.

Owing to the particularconnection between the pawl I and its operating handle or pedal, the pivot of said handle or pedal is located more to the rear of the pivotal connection a between the supporting-frame and the seatframe when the footboard is in its lowest position than would be the case were said handle or pedal secured directly upon the rockshaft I of the pawl. In this way a greater leverage is attained and the footboard may be elevated with greater case. A similar result may be attained by the modified construction shown in Fig. 9, in which the link J is dispensed with and the pawl I is carried on the same shaft J to which the operatinghandle J is secured, said shaft being disposed obliquely relatively to the side arms A A, as shown.

The side arms A A of the footboard-supporting frame are preferably extended, as at A a short distance above the pivotal connection a of these arms with the seat-frame B, the object of this being to cover up the space which would otherwise be left between the said arms and the seat-frame when the footboard is elevated to its highest position. The upper extensions A of the side arms project into slots or recesses Z in the wood base portion or frame L of the upholstered chairseat L, which rests upon the metallic seatframe B.

I will now proceed to describe my improved back-rest as follows: The hinged connection between the back-supporting frame and the seat-frame is substantially the same as that shown and described in my before-mentioned patent, as is also the locking mechanism for holding the back-supporting frame in any position to which it may be inclined; but the means for actuating said locking mechanism is different. The back-rest-supportin g frame N consists of two connected side or guide rails N N, straight for the greater portion of their length, but at their lower ends curved in the arc of a circle to form an arc-shaped hinge member N This arc-shaped hinge member N is adapted to fit and move in or upon a corresponding arc-shaped hinge member N fixed upon the seat-frame B. The arc-shaped hinge members are formed with suitable interlocking guide grooves and tongues to guide and hold the parts in proper relation to each other. A pawl N is keyed upon a rock-shaft N journaled upon the back-supporting frame in lugs 0 n, the pawl being provided with teeth for engaging a series of notches n on the fixed hinge member N A plate-spring N secured to the pawl N and bearing against a portion of the backsupporting frame, serves to keep the pawl engaged with the series of notches 01, except when said pawl is purposely withdrawn therefrom.

The improved means for actuating the pawl N for withdrawing the same from looking engagement with the fixed hinge member for permitting the back-frame to be tilted backward and forward is as follows: A bell-crankcontrolling lever O is pivoted at 0 to one of the side rails N of the back-supporting frame, near the top thereof, with its long arm 0 projecting slightly beyond the side of the side rail of the supporting-frame to which it is pivoted. To the inner or short arm 0 of the controlling-lever is connected one end of a connecting rod or link 0 the opposite end of which is connected to an arm 0 keyed upon the rock-shaft N, to which the pawl N is also keyed. Pressure upon the long arm 0 of the controlling-lever rocks its inner or short arm 0 which motion is transmitted to the arm 0 by the connecting-rod O and the pawl N is rocked downwardly out of engagement with the fixed hinge member.

Itshould be observed that the controllinglever O of the back-frame-locking mechanism is located at a point where the back-frame is grasped by the hands of the operator when it is desired to change the angle or inclination of the same and that when the backframe is so grasped one hand of the operator covers the projecting arm of the controllinglever, and a slight and natural pressure of this hand upon the controlling-lever quickly releases the locking mechanism, and the backframe may be rocked backward or forward, as desired. When the desired inclination or adjustment of the back-frame has been attained, the operator simply releases his hold of the same and the locking mechanism automatically acts to instantly look the backframe in its adjusted position. Thus the adj ustment of the back-frame may be quickly and easily effected by inclining it forward as well as backward without the necessity of manipulating any handles, screws, or levers, save the rocking of the controlling-lever, which, as before stated, may be performed by the same movement of the hand required for grasping and moving the back-frame.

A vertically-ad j ustable back-pad carrier or frame P is suitably mounted to be moved up and down upon the back-supporting frame, and a back-pad P is hinged to the top of said frame; but as the construction of these particular parts of the chair form no part of my present invention description of them is unnecessary.

For the purpose of quickly and automatically elevating the footboard to its uppermost position when it is desired to place the chair IIO in its aforesaid anaesthetic position I have provided mechanism whereby when the backrest section of the chair is lowered to a level with the chair-seat the footboard is automatically raised to a level with said seat. I am aware that such a movement is not broadly new; but I have devised novel and improved means for accomplishing it, which I will now describe.

A link R, passing from 'front to rear of the seat-frame of the chair, is pivoted at its forward end to the footboard-supporting frame a short distance below its pivotal connection a with the seat-frame B. Said link is shown as being pivoted between lugs a on the inner side of the central plate or screen A of the footboard supporting frame. The link is prevented from falling by means of a side lug 4" near its rear end resting and adapted to travel upon the curved flange or ledge s of a guide-plate S, secured to the seat-frame. The rear extremity of the link is notched at r for engagement with a stud n on one of the side rails N of the back-rest-supporting frame, near the lower extremity thereof.

Without further description it will be apparent that the back-rest may be adjusted or rocked back and forth within certain limits to secure all necessary or desired operating positions without affecting or moving the footboard and that the footboard may likewise be raised and lowered to secure various operating positions without affecting the back-rest. The moment, however, the back is lowered to or beyond the limit of its operating positions its stud 72 comes in contact with the notched end of the link R, which transmits the continued downward movement of the back-rest to the footboard, whereby the latter is raised to the level of the chair-seat simultaneously with the lowering of the backrest to the level of said seat. After the backrest has been moved to a level with the chairseat and the lever 0 released, the back-rest and of course the footboard are securely locked in position. \Vhen the back is again raised to the point where its operating positions begin, the footboard is automatically lowered to the beginning of its medium or operating position, at which point the back and the footboard are again independently adjustable.

The guide S not only serves to prevent the link R from falling when its notched end is not engaged by the stud n of the back-rest, but it also maintains said link in the proper position to insure the contact or engagement of the stud and notched link in whatever position they may happen to be when it is desired to elevate the footboard by means of the back-rest.

The number and arrangement of the teeth on the rock-plate E of the main controllingrod is such that the pawl does not act after the footboard has been elevated a certain distance-say about midway between its highest and lowest positions. By this means the footboard may be adjusted to and locked in any desired operating position of vertical adj ustment from its lowest to its medium positions in which it is to be used as a foot board or rest by its operating-treadle and lockingpawl; but after the footboard is raised to its highest position to form a leg-rest, as previously explained, it will freely move to its medium position when the back-rest is raised to the beginning of its operating position.

As shown in Fig. 2, the seat-frame B of the chair is,as usual, j ournaled to rock about trunnions t t of a yoke or cross-head T, connected to the upper end of a chair-body-supporting plunger U. In Figs. 3 and 4. I have shown an improved connection between the seatframe and the yoke or cross-head. In this improvement instead of journaling the yoke directly to the sides of the seat-frame, as is customary, it is journaled to trusses B B, which extend from front to rear of the seatframe near and substantially parallel with the sides of said frame. These trusses B B are bowed or curved upwardly, as shown in Fig. 4, in order that their central portions, to which the yoke is journaled, may extend above the top of the seat-frame. The trusses are shown as being cast integral with the seatframe, although, if desired, they maybe made separate and bolted to the seat-frame. This construction not only provides a stronger and more rigid seat-frame, but it permits of the use of a shorter yoke or cross-head, which obviousl has less spring or yield than the OOmparatively long cross-heads now in common use. Moreover, this construction enables the trunnions to be located above the seat-frame B and between the frame L of the upholstered seat L, thus elevating the trunnions and bringing them nearer the center of weight of the chair-body and patient, whereby the chairbody is more evenly balanced.

The dental chair herein shown and described represents but a single embodiment of my invention, together with some slight modifications; but it is obvious that my invention is susceptible of many variations without departing from the scope of my invention, and I therefore do not wish to be understood as being confined to the precise de tails of construction herein shown and described.

I claim as my invention-- 1. The combination with the seat of a dental chair, of the footboard-supporting frame hinged thereto, the footboard hinged to the lower end of said frame, means for maintaining the parallelism of said footboard relatively to said seat when the former is vertically adjusted, a foot-rest carried at the outer end of the footboard and normally occupying a position above the level of the plane of the same, and means for automatically moving the foot-rest into a position on a level with or below the upper surface of the footboard when said footboard is moved into a position on a level with said seat, substantially as and for the purpose described.

2. The combination with the seat of a dental chair, of the footboard-snpporting frame hinged thereto, the footboard hinged to the lower end of said supporting-frame, a footrest hinged to the outer end of said footboard and normally occupying a position above the level of the same, a main controlling-rod pivoted to said seat and to said footboard, a secondary controlling-rod pivoted to the main controlling-rod and to the foot-rest, whereby when the footboard is raised to the level of the seat, the foot-rest is automatically moved into a posit-ion on a level with the footboard, and means for locking the footboard in any position to which it may be adjusted, substantially as and for the purpose described.

3. The combination with the seat of a dental chair, of the footboard-snpporting frame hinged thereto, the vertically-adjustable footboard hinged to the lower end of said footboard-frame, mechanism for locking the footboard in its vertically-adjusted position, and a lever located substantially on a line with the plane of said footboard for controlling said locking mechanism and by means of which the footboard may be raised and lowered, substantially as and for the purpose described.

4. The combination with the seat of a dental chair, of a footboard-supporting frame hinged thereto, a vertically-adjustable footboard hinged to the lower end 'of said supporting-frame, a controlling-rod pivoted to said seat and to said footboard, a rack upon said controlling-rod, and a rocking pawl carried by said supporting-frame, substantially as and for the purpose described.

5. The combination with the footboard of a dental chair, of a foot-rest pivoted to the outer end thereof, means for sustaining said footrest in an upright operative position above the level of said footboard, and means where by said foot-rest may be caused to drop into an inoperative position to or below the level of said footboard, substantially as and for the purpose described.

6. The combination with the footboard of a dental chair, of a foot-rest pivoted to the outer end thereof, and a toggle-lever connection between said footboard and said foot-rest,

whereby when the toggle-lever is straight ened out the foot-rest is sustained in an upright operative position above the level of the footboard and when the toggle-lever is opened the foot-rest is permitted to drop to or below the level of the footboard into an inoperative position, substantially as and for the purpose described.

7. The combination with the seat of a dental chair, of a footboard-supporting frame hinged thereto, a footboard hinged to the lower end of said supporting-frame, a footrest pivoted to the outer end of said footboard, a main controlling-rod pivoted to said chair-seat and to said supporting-frame, a secondary controlling-rod connected at one end with said main controlling-rod, and a toggle-lever connection between the opposite end of said secondary controlling'rod and said foot-rest, whereby when said toggle-lever connection is straightened out the foot-rest is normally sustained in an upright operative position above the level of said footboard and when said footboard is raised to its uppermost position on a level with said chair-seat the foot-rest is automatically moved to a position on a level with or below the surface of said footboard, and when said toggle-lever connection is opened or broken the said footrest drops to or below the level of the footboard independentlyof the movement of said footboard, substantially as described.

8. The combination, in a dental chair, of the footboard,the foot-rest pivoted to the outer end thereof and adapted to normally occupy an operative position above the level of said footboard, and a supplemental foot-rest pivoted to the outer end of said foot-rest, and adapted to be turned into two operative positions nearer to and farther away from the footboard, by rocking it about its pivotal connection with said foot-rest, substantially as and for the purpose described.

9. The combination, in a dental chair, of the metallic seat-frame, an upholstered seat fitted thereon, and provided with a wood base having slots or recesses in its opposite sides, a footboard and side arms forming the supporting-frame for said footboard and pivoted to said metallic seat-frame, said side arms extending a short distance above their pivotal connections with said metallic seat-frame, said extensions being adapted to enter the slots or recesses in the Wood base of the upholstered seat when the footboard is in any of its low positions, substantially as and for the purpose described.

10. The combination, in a dental chair, of the seat, a back-supporting frame hinged thereto and adapted to be rocked vertically,

' means for lockin g said back-supporting frame in any position to which it may be rocked, and a controlling'handle pivoted to said back supporting frame to rock transversely thereof, whereby said locking means may be controlled by moving said lever transversely of the back-supporting frame, substantially as and for the purpose described.

11. The combination, in a dental chair, of the seat, a back-supporting frame hinged thereto and adapted to be rocked vertically, an automatic lock for normally locking said back-supporting frame in any position to which it may be rocked, a controlling-lever for said lock pivoted to said back-supporting frame and having its handle projecting from the side thereof, whereby when the handle of said controlling-lever is pressed inward, the lock is released and the back-supporting frame is free to be rocked vertically, substan= tially as described.

12. The combination, in a dental chair, of the seat provided with a fixed arc-shaped hinge member having detent-notches therein, a back-supporting frame provided with an arc-shaped hinge member having sliding connection with said fixed hinge member, a pawl pivoted to said back-supporting frame and normally in engagement with the detentnotches of said fixed hinge member, a controlling-lever pivoted to said back-supporting frame near its. upper end and having its handle projecting from the side thereof, and a connection between said pawl and said controlling-lever, whereby when the handle of the latter is pressed inward the pawl is disengaged from the notches of the fixed hinge member, substantially as and for the purpose described.

13. The combination, in a dental chair, of the seat, a vertically-adjustable footboard hinged to the frontthereofl-a foot-rest car- 7 ried at the outer end of said footboard and normally occupying a position above the level of the same, a back-rest hinged to the rear of said seat-frame, and connections between said back-rest and said footboard and between said footboard and said foot rest, whereby the back rest and the footboard may be independently adjusted to various operating positions within certain limits, but when the back-rest is lowered to a level with the seat, the footboard is automatically elevated to a level with said seat and said backrest, and the foot-rest is automatically lowered to or below the level of said footboard, to bring the back-rest, the seat, the footboard and the foot-rest into alinement,substantially as and for the purpose described.

14. The combination, in a dental chair, of the seat, a vertically-adjustable footboard hinged to the front thereof,a back-rest hinged to the rear of said seat and adapted to rock vertically, both the back-rest and the footboard being capable of adjustment to a level with said seat, a link pivoted to the footboard and provided with a side lug, and having its rear end notched, a fixed guide-plate having a curved flange or ledge upon which the said side lug of the link rests and travels and a stud on the back-rest adapted to engage the notched end of said link, whereby when the back-rest is lowered to a level with the seat the foot-rest is thereby automatically elevated to a level with said seat, substantially as and for the purpose described.

15. The combination, in a dental chair, of the seat-frame, trusses extending from front to rear thereof and substantially parallel with the sides of said frame, said trusses also ex- 

